1. Field pertinent to the Invention
The present invention relates to a method for forming a coating film, in which a coating composition having high adsorbability to a silicone protective film formed for protecting a vapor deposition layer formed on a surface of a base material is made to adhere to the surface of the silicone protective film, and a vehicle lamp device formed by the method.
2. Description of the Related Art
A general technique for making a coating composition adhere to a surface of a silicone protective film formed for protecting a vapor deposition layer formed on a surface of a base material, that is, for example, a general technique for coating a base material constituting a reflector, an extension reflector, or the like, in a vehicle lamp device used as a car head lamp, or the like, will be described with reference to FIG. 4.
First, to secure the surface smoothness of a base material 10 made of a material such as synthetic resin and enhance the adsorbability of a vapor deposition layer 12, an undercoat layer 11 is provided on a surface of the base material 10 and then the vapor deposition layer 12 of an aluminum vapor deposition film is formed on a surface of the undercoat layer
Further, to protect the vapor deposition layer 12 to thereby secure weather resistance, a silicone protective film 13 is formed as a top coat on a surface of the vapor deposition layer 12 by a spray coating method or by a method to which plasma polymerization disclosed in JP-A-10-147876 is applied.
Color coating (enamel coating) 14 such as black coating, silver metallic coating, or the like, is applied onto a surface of the top coat constituted by the silicone protective film 13 for the purpose of enhancing weather resistance and external appearance or the like.
However, when a coating composition such as two-fluid uretahne heretofore generally used was used for color coating 14 applied onto the surface of the silicone protective film 13, there was a technical problem that the coating composition was apt to be peeled in the interface between the coating composition and the silicone protective film 13 because the adsorbability of the coating composition to the silicone protective film 13 was insufficient.
Therefore, an object of the present invention is to provide a method for forming a coating film by using a coating composition highly adsorbable to a silicone protective film, and a vehicle lamp device formed by the coating film-forming method.
To achieve the foregoing object, the present invention employs the following means.
According to a first aspect of the present invention, there is provided a method for forming a coating film which uses means of making a siloxane bond (Sixe2x80x94O bond)-containing coating composition adhere to a surface of a silicone protective film which is formed for protecting a vapor deposition layer formed on a surface of a base material.
In this means, lone-pair electrons of oxygen atoms constituting siloxane bonds are coordinated so as to be bonded to silicon atoms (Si) contained in the silicone protective film so that the adsorbability of the coating composition to the silicone protective film is enhanced to prevent the coating composition from being peeled.
According to a second aspect of the present invention, in the method for forming a coating film, the silicone protective film stated in the first aspect is formed by using a plasma polymerization method.
In the means using such a plasma polymerization method, the adsorbability of the coating composition to the silicone protective film can be enhanced more greatly because the silicone protective film can be formed with a more uniform film thickness compared with the spray coating method.
According to a third aspect of the present invention, in the method for forming a coating film stated in the first or second aspect, an acrylic silicone coating composition is used as the coating composition.
In this means, the adsorbability of the coating composition to the silicone protective film can be secured because terminal oxygen atoms of siloxane bonds (Sixe2x80x94O bonds) crosslinking polyacrylic chains to one another are coordinated so as to be bonded to silicon atoms (Si) contained in the silicone protective film.
According to a fourth aspect of the present invention, in the method for forming a coating film, the acrylic silicone coating composition stated in the third aspect is made to contain an ultraviolet light absorber which is hard to volatilize.
In this means, attention is paid to the fact that an ultraviolet light absorber such as a benzophenone compound contained, to fulfill a function of preventing deterioration due to the sun light, in an acrylic silicone coating composition which is widely used as a coating composition for the exterior of a car, the outer wall of a building, or the like, has such characteristic that the ultraviolet light absorber is apt to volatilize in the condition of 80xc2x0 C. or higher. Therefore, measures to change the ultraviolet light absorber to a new one hard to volatilize are taken so that the method can be applied safely to a member placed in a high-temperature environment.
According to a fifth aspect of the present invention, in the method for forming a coating film, only a benzotriazole compound is specifically used as the ultraviolet light absorber stated in the fourth aspect. In this means, measures are taken so that the method can be applied safely to a member such as a reflector, an extension reflector, or the like, disposed in the inside of a lamp chamber of a vehicle lamp device, or the like, exposed to a high temperature of 120xc2x0 C. or higher by heat of a lamp.
According to a sixth aspect of the present invention, in a vehicle lamp device having a front lens permeable to ultraviolet light, a coating film is formed on a member irradiated with ultraviolet light transmitted through the front lens and incident on the member, by using the coating film forming method stated in the fourth or fifth aspect.
In this means, an ultraviolet light absorber hard to volatilize even in a high-temperature environment is contained in a coating composition used for forming a coating film on a vapor deposition film on a member such as a reflector, an extension reflector, a dummy reflection portion, or the like, disposed in the inside of a lamp chamber exposed to such a high-temperature environment by heat of a lamp. Hence, the ultraviolet light absorber is prevented from volatilizing so that the front lens does not get fogged and, at the same time, deterioration due to ultraviolet light is prevented.
As described above, in the coating film-forming method according to the present invention, a coating film highly adsorbable to a silicone protective film for protecting a vapor deposition layer made of an aluminum vapor deposition film, or the like, can be formed. Hence, the method widely contributes to development of coating film-forming techniques in a vehicle lamp device for a car, or the like. Moreover, in various members each coated with the coating film by the coating film-forming method according to the present invention, the coating composition is hard to peel. Hence, the method has a technical significance that products such as a vehicle lamp device, etc. excellent in weather resistance, durability and damage resistance can be provided.